Macrocyclization on the fullerene core: Direct regio‐ and diastereoselective multi‐functionalization of [60]fullerene, and synthesis of fullerene‐dendrimer derivatives

Abstract

The macrocyclization between buckminsterfullerene, C,,, and bis-malonate derivatives in a double Singe1 reaction provides a versatile and simple method for the preparation ofcovalent bis-adducts of C,, with high regioand diastereoselectivity. A combination of spectral analysis, stereochemical considerations, and X-ray crystallography ( Fig. 2 ) revealed that out of the possible in-in, in-out, and out-out stereoisomers, the reaction of bis-malonates linked by 0-, ni-, or p-xylylene tethers afforded only the out-out ones (Scheme I). In contrast, the use of larger tethers derived from 1,lO-phenanthroline also provided a first example, (*)-19 (Scltemr 2), of an in-out product. Starting from optically pure bis-malonate derivatives, the new bis-functionalization method permitted the diastereoselective preparation of optically active fullerene derivatives (Schemes 4 and 5 ) and, ultimately, the enantioselective preparation (enantiomeric excess ee > 97 YO) of optically active cis-3 bis-adducts whose chirality results exclusively from the addition pattern (Fig. 6). The macrocyclic fixation of a bis-malonate with an optically active, 9,9-spirobi[9H-fluorene]-derived tether to C,, under generation of 24 and ent-24 with an achiral addition pattern (Scheme 4 ) was found to induce dramatic changes in the chiroptical properties of the tether chromophore such as strong enhancement and reversal of sign of the Cotton effects in the circular dichroism (CD) spectra (Figs. 4 and 5). By the same method, the functionalized bis-adducts 50 and 51 (Schemes 10 and If) were prepared as initiator cores for the synthesis of the fullerene dendrimers 62, 63, and 66 (Schemes 12 and 13) by convergent growth. Finally, the new methodology was extended to the regio-and diastereoselective construction of higher cycbpropanated adducts. Starting from mono-adduct 71, a clipping reaction provided exclusively the all-cis-2 tris-adduct (&)-72 (Scheme 14), whereas the similar reaction of bis-adduct 76 afforded the all-cis-2 tetrakis-adduct 77 (Scheme 15). Electrochemical investigations by steady-state voltammetry (Table 2) in CH,CI, ( + 0 . 1~ Bu,NPF,) showed that all macrocyclic bis(niethan0)fullerenes underwent multiple reduction steps, and that regioisomerism was not much influencing the redox potentials. All cis-2 bis-adducts gave an instable dianion which decomposed during the electrochemical reduction. In CH,CI,, the redox potential of the fullerene core in dendrimers 62, 63, and 66 is not affected by differences in size and density of the surrounding poly(ether-amide) dendrons. The all-cis-2 tris-and tetrakis(methano)fullerenes (5)-72 and 77, respectively, are reduced at more negative potential than previously reported all-e tris-and tetrakis-adducts with methano bridges that are also located along an equatorial belt. This indicates a larger perturbation of the original fullerene rr-chromophore and a larger raise in LUMO energy in the former derivatives.') Present address: Groupe des Matkriaux Organiques,

Synthesis and Orthogonal Functionalization of [60]Fullerene e,e,e‐Trisadducts with Two Spherically Defined Addend Zones

“…Regioselective formation of e,e,e-trisadducts based on tripodal malonate tethers: To achieve straightforward access to a great variety of structurally tunable e,e,e-trisadducts containing diverse functionalities, a synthetic concept that fulfills the following aspects has to be implemented: 1) the use of readily accessible precursors that preorganize the malonate units in an appropriate manner, 2) highly regioselective cyclopropanation reactions that lead to e,e,e-trisadducts in good yields, 3) the facile removal of the structural template by appropriate deprotection strategies, 4) the possibility of further functionalization of deprotected derivatives, and 5) complete control of in/out isomerism [35] in case of asymmetrically substituted malonates. Based on these considerations, we chose a 1,3,5-trisubstituted benzene core as the most prominent structural template.…”

Modulating Charge‐Transfer Interactions in Topologically Different Porphyrin–C60 Dyads

“…[20,21] Modeling of doubly linked porphyrin ± fullerene dyads suggests the use of meta-rather than para-substituted adducts.…”

Bismalonates Constructed on a Hexaphenylbenzene Scaffold for the Synthesis of Equatorial Fullerene Bisadducts

“…[7] Interestingly, compound 1 shows enhanced optical-limiting properties when compared to a 1:1 mixture of the separated components. When the two moieties are covalently linked, deacti-two cyclopropane rings on the C 60 core was determined on the basis of the molecular symmetry (C 1 ) deduced from the 1 H and 13 C NMR spectra and further confirmed by the characteristic features seen in their UV/Vis spectra.…”